Spin Coating SOP (UWaterloo)

Purpose

To apply a uniform photoresist coating on silicon wafers using a calibrated spin-coater for microfabrication and lithography processes.

This SOP supports HackerFab lithography workflows targeting <10 µm features, consistent with recent calibration results.

Currently, our spin coater has an error tolerance of <0.3%

With the new build, error tolerance will be even lower!

Scope

Applies to:

• Silicon wafers (1cm x 1cm diced samples)

• Positive photoresist

• HackerFab custom spin-coater

Used before:

• UV lithography

• Pattern transfer

• Etching or lift-off

Equipment & Materials

Equipment

• HackerFab calibrated spin-coater

• Hot plate

• Micropipette or resist dropper

• Wafer tweezers

• Timer

• Fume hood or wet lab bench

Materials

• Silicon wafers

• Photoresist (AZ-P4620)

• Acetone

• IPA

• DI water

• He gas

Safety Precautions

Work inside fume hood. Wear gloves, goggles, lab coat.

Photoresist solvents are flammable and toxic.

If using developers or etchants later (KOH, HF etc.), follow separate SOPs.

Dispose waste in labeled resist-waste container.

Process Parameters

(Fill based on your calibrated spin-coater data)

Step	Parameter	Typical Value
Clean	DI water rinse	10s
Clean	Acetone rinse	10s
Clean	IPA rinse	10s
Dry	He blow dry	Until dry
Spin step 1	Spread speed	500 rpm, 5s
Spin step 2	Final speed	5000 rpm, 30s
Soft bake	Temp; Time	100°C; 1min

Procedure

Wafer Cleaning

1. Rinse wafer with DI Water.

2. Rinse wafer with acetone.

3. Rinse with IPA.

4. Blow dry with Helium.

5. Inspect wafer for particles.

Spin Coating

1. Place wafer on spin-coater chuck.

2. Dispense ~1 mL photoresist at wafer center.

3. Run spin program:

   • Spread: 500 rpm for 5 s

   • Spin: 4500-5000 rpm for 30 s

4. Stop spin-coater.

5. Remove wafer carefully.

Soft Bake

1. Place wafer on hot plate at 100 °C.

2. Bake for 60 s.

3. Cool wafer on clean surface.

Expected Results

• Uniform resist thickness.

• No streaks or bubbles.

• Good adhesion.

• Compatible with UV lithography, achieving <10 µm features.

Troubleshooting

Problem	Cause	Fix
Edge bead	Too much resist	Use less resist volume
Streaks	Dirty wafer	Improve cleaning
Non-uniform thickness	RPM mismatch	Recalibrate spin-coater
Bubbles	Moisture	Dehydrate bake wafer

Notes

• Use tachometer-verified RPM values